Black-and-white images formed in a photographic process are generally produced by developing silver halide in a black-and-white developer to form a silver image. A black-and-white developer, such as hydroquinone, is commonly used to reduce the exposed silver halide to silver metal. The undeveloped silver halide is removed from the print by `fixing` with aqueous sodium thiosulfate. The silver metal remaining in the print represents the image.
In the photographic industry, a motion picture film processing laboratory who wishes to produce both black-and-white and color pictures must have separate processing systems; one for color and one for black-and-white, as the two systems are not compatible. It would, therefore, be advantageous for the processing laboratory to have one process capable of producing either black-and-white or color pictures.
U.S. Pat. No. 4,348,474--Scheerer discloses a system wherein black-and-white images are formed by the use of one emulsion that is treated with three sensitizing dyes.
U.S. Pat. No. 2,186,736--Schneider discloses the use of several color components in one layer for a black-and-white image formation.
U.S. Pat. No. 2,592,514--Harsh discloses a color film in which couplers forming more than one color are present in the same layer of the color film.
There have been commercialized products that have formed black-and-white images by the use of pan sensitized emulsions which contain three spectral sensitizing dyes, color dye-forming couplers and one emulsion. These pan-sensitive emulsions are sometimes coated in a fast and a slow layer to form images after exposure and development of the couplers. While the above products are somewhat successful, they do not achieve a neutral image. Additionally, the tone reproduction of such materials is severely limited by the contrast range of the emulsion.
U.S. Pat. No. 5,362,616--Edwards et al. discloses a system for forming black-and-white images on photographic paper through the use of color processing. The system utilizes a spectrally sensitized silver chloride emulsion containing one spectral sensitizing dye that is combined in the same layer with a mixture of cyan, magenta, and yellow dye-forming couplers. In a preferred form there is one silver chloride emulsion layer sensitized to blue light, one silver chloride emulsion layer sensitized to green light, and one silver chloride emulsion layer sensitized to red light, with each emulsion layer containing a mixture of the cyan, magenta, and yellow dye-forming couplers.